CVE-2026-101984 in Junos OS
Summary
by MITRE • 10/14/2026
A Reachable Assertion vulnerability in the routing protocol daemon (rpd) of Juniper Networks Junos OS and Junos OS Evolved allows a network-adjacent BGP peer to cause a denial of service when labeled-unicast aggregate-label is configured.
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Analysis
by VulDB Data Team • 10/14/2026
The identified security flaw resides within the Routing Protocol Daemon, known as rpd, which serves as the core component responsible for managing routing protocols in Juniper Networks Junos OS and Junos OS Evolved environments. This specific vulnerability manifests as a reachable assertion failure triggered under precise configuration conditions involving labeled-unicast aggregate-label settings. The presence of this feature indicates that the network infrastructure is configured to support Multiprotocol Label Switching (MPLS) or similar label-based forwarding mechanisms, which are critical for modern service provider and enterprise backbone networks requiring traffic engineering and efficient path selection.
The technical nature of this vulnerability centers on a logic error within the BGP peer processing routines when handling specific route advertisements associated with labeled-unicast aggregates. When a network-adjacent Border Gateway Protocol (BGP) peer sends crafted or malformed update messages that interact with the aggregate-label configuration, the rpd process encounters an unexpected state during validation checks. Instead of gracefully rejecting the invalid input or handling it through standard error recovery mechanisms, the daemon triggers an assertion failure. In software engineering terms, an assertion is a sanity check used to verify assumptions made by the programmer; when these assertions fail in production code without proper exception handling, they typically result in immediate process termination. Consequently, this leads to a crash of the rpd service on the affected device.
The operational impact of this vulnerability is severe due to its potential for causing a denial of service against critical network infrastructure. Since BGP is fundamental to internet routing and inter-domain connectivity, crashing the daemon responsible for maintaining these sessions can result in significant disruption. Depending on the high-availability configuration of the router, such as redundant route engines or chassis clustering, the impact may range from a temporary loss of specific routes to a complete node failure if redundancy mechanisms are not properly configured or also affected by the crash. This allows an attacker with network adjacency to destabilize routing tables, potentially causing traffic blackholes, increased latency, or total connectivity loss for downstream networks relying on the compromised device for path information.
From a threat modeling perspective, this vulnerability aligns with CWE-617, which describes Reachable Assertion issues where code execution can trigger an assertion failure leading to denial of service. In terms of attack vectors and tactics, it corresponds to MITRE ATT&CK techniques related to Resource Hijacking or Denial of Service via network-based exploitation. The requirement for the attacker to be a BGP peer implies that they must have direct IP connectivity to the router's management or peering interfaces, restricting the threat model primarily to insider threats or adversaries who have compromised adjacent systems within the same autonomous system or trusted peering relationship.
Mitigation strategies should focus on both immediate remediation and long-term architectural hardening. The primary defense is applying the vendor-provided software patches that address this specific assertion failure in rpd. Administrators must ensure their Junos OS and Junos OS Evolved installations are updated to versions where this flaw has been resolved. In environments where patching cannot be immediately performed, network segmentation should be enforced to restrict BGP peering sessions only to trusted peers with verified identities. Additionally, implementing strict route filtering policies using prefix-lists and AS-path filters can help mitigate the risk by preventing malformed or unexpected updates from reaching the vulnerable processing logic. Regular monitoring of system logs for rpd restarts or assertion messages is also recommended to detect potential exploitation attempts early.